YouTuber's seven-day water fast produced dramatic short-term effects and renewed debate over risks

Justin Dorff, a Pennsylvania-based health coach and social media creator, said a seven-day water-only fast left him exhausted for several days before he experienced a sudden surge of energy, lost more than 10 pounds and reported a marked reduction in junk-food cravings. Dorff, 42, documented the challenge in a YouTube video that has attracted tens of thousands of views and detailed his physical and mental experience hour by hour.

Dorff — who has built a following by testing extreme nutrition and longevity regimens — told viewers he began the fast after weeks of low energy, nagging injuries and persistent cravings. He said he tracked mood, cravings, hunger and energy during the seven-day “Great Reset.” He reported the first 20 hours were largely uneventful, but the second and third days brought headaches, nausea and severe fatigue. Days three and four, he said, were “fantastically rough,” with cold hands and feet and low mood. He described a turning point on day five, when he awoke with renewed focus and what he called “tons of energy.” By day six his weight had dropped from about 148.1 pounds to 139.6 pounds, and by the end of the fast he said he had lost more than 10 pounds and about 10.5 inches around his waist.

During the challenge Dorff said he used multivitamins, electrolyte capsules and salt water to manage headaches and sustain himself. He said the evenings were the hardest, with hunger and cravings worst while his energy and mood were lowest, but that by the latter half of the week he was able to complete workouts and focus normally.

Intermittent fasting and longer fasts have been promoted by some researchers and high-profile advocates as a way to improve metabolic markers, reduce weight and stimulate cellular processes such as autophagy, in which cells remove damaged components. Supporters point to studies suggesting benefits from time-restricted eating and short-term fasting for glucose control and weight loss. The practice shot to wider public attention in the early 2010s and has been adopted in various forms by celebrities and influencers.

Medical experts and researchers caution that fasting effects vary by individual and that longer or repeated prolonged fasts carry risks. Physicians have warned that extended calorie abstention can prompt the body to use stored glycogen and then fat for fuel, increasing ketone production. While moderate ketone production is part of normal metabolic adaptation, very high levels can lead to ketoacidosis, a dangerous rise in blood acidity that requires medical treatment. Some studies and clinicians have also raised concerns that prolonged or extreme fasting could increase cardiovascular risk in certain populations or trigger digestive and metabolic problems when not supervised.

Experts emphasize that fasting frequently leads to large calorie intakes during refeeding periods for some people, which can blunt weight-loss benefits. Others note that sustained autophagy beyond short, controlled periods has not been proven safe and could, in theory, damage organs if cellular degradation becomes excessive. The diversity of study designs, participant profiles and fasting protocols has produced mixed evidence, leaving open questions about long-term outcomes.

Dorff framed his fast as an attempt to reset body, mind and spirit rather than a medical intervention. He has portrayed similar experiments on his channel before, including restrictive short-term diets and a trial of an intensive anti-ageing routine developed by another wellness entrepreneur. His account adds to a growing number of firsthand reports that emphasize variability in how people feel during different phases of fasting: an early period of fatigue and hunger followed, for some, by a later period of increased energy and alertness.

Clinicians advise that anyone considering extended fasting consult a medical professional, particularly people with chronic conditions, those taking medications, older adults, and pregnant or breastfeeding women. Hydration, electrolyte balance and monitoring are commonly cited as essential components of safer supervised fasting protocols. Public-health guidance generally supports structured, evidence-based approaches to weight management and metabolic health, including balanced diets, physical activity and medical oversight when interventions go beyond short-term time-restricted eating.

As fasting remains a popular wellness trend, researchers say more large, long-term randomized trials are needed to clarify who may benefit, what regimens are safe, and what risks may accrue over time. Dorff’s video, and others like it, underscore both the appeal of personal experiments in wellness and the continuing scientific debate about the benefits and hazards of prolonged food abstention.